The present invention concerns a connector for adapting a tip to a liquid transfer device, particularly one for the transfer of liquid medicine.
Different means for connecting tips to liquid transfer devices are already known. One of these is described in U.S. Pat. No. 4,596,561, in which the transfer device is a prefilled single-dose hypodermic syringe and the tip is a needle connected to a cover adapted to a needle-holding ferrule disposed at the end of the syringe body.
One critical problem posed by these devices is that of unused contents, i.e., the quantity of medication remaining in the syringe after injection. The problem is particularly acute when the device is provided with a connector with a standard truncated Luer cone body of exterior dimensions approaching a 4 mm diameter and with a divergence of 6% along a length of from 7 to 10 mm. These exterior dimensions are necessary to allow the device to be attached to the standard female tips associated with such various elements as needles, multi-track valves, catheters, etc. In known manner, this standard truncated connecting device currently called the "conical Luer 6% connecting device" has a central conduit for the passage of liquid. Furthermore, it is known to be technically impossible to produce such a tip efficiently by means of thermoplastic injection molding when the central conduit has a relatively narrow ferrule, as the walls of the cone body then become proportionately too thick, thereby slowing down the injection cycle of the thermoplastic material considerably so that the cooling period for the material must be greatly increased to avoid shrinking.
To achieve a ferrule of the Luer type with a central canal diameter of the order of 0.4 mm, so as to result in relatively small amount of unused contents, the walls of the cone body should be a minimum of about 1.8 mm thick. This considerable thickness would require the synthetic material to undergo a lengthy cooling phase, during which bubbles would tend to form. Therefore, it would be nearly impossible to adhere to the parameters fixed by international norms for truncated male Luer 6%-type ferrules.
This is the reason that injection-manufactured disposable syringes presently in commerical use have a Luer ferrule axially transvered by a central conduit with a diameter of the order of 3 mm, thereby permitting the walls to be thinner, of the order of 0.5 mm. This technological and economic imperative has the unfortunate result of leaving a larger quantity of unused contents inside the axial conduit of the ferrule.
This problem of unused contents has been approached and partially resolved by a device described in European Pat. Application published as No. 47042. The unused contents created by the relatively large dimensions of the axial conduit disposed inside the needle-holding ferrule of the syringe is partially overcome by insertion, during the final operation, of a truncated element connected to the piston extremity. However, this system does not resolve the problem of the standard unit described above, known as the Luer 6% truncated unit. In practice, when a truncated female element is adapted to a truncated male Luer 6% ferrule, a space always remains between the base of the female element and the extremity of the male ferrule, thereby affording little control over the amount of unused contents, a situaton which is both bothersome and dangerous, although useful in certain cases to serve as a viewing chamber for observing the passage of the liquid.
U.S. Pat. No. 4,240,425 proposes a unit which almost completely eliminates the problem of unused contents in injection syringes by providing on the one hand, a connecting device comprising a hollow tubular ferrule and on the other hand, a needle-bearing flange of essentially complementary shape adaptable to the said ferrule. The disadvantage of the this system resides in the fact that said needle-holding flange does not correspond to standard construction and therefore prevents replacement of the specialized needle by a standard needle if for some reason the special needle cannot be used. Actually, if a standard needle comprising a Luer 6% flange is placed in the ferrule of this syringe, the problem of unused contents described above surfaces again, and the patient is not injected with the prescribed dose of medication.